Seattle Mayor Mike McGinn issued an order that allowed police to confiscate items that could be used as weapons. Items include large dowels, handles for signs, ball peen hammers and tire irons.

McGinn said the problems began when a group of about 75 “Black Bloc”-type protesters joined the crowd at Westlake Plaza and left a trail of vandalism from Third to Sixth avenues using hammers, tire irons, paint, incendiary devices and solid rods. McGinn said the rods, which are 3 inches wide, 5 feet long and "quite heavy" doubled as sign posts and were used to shatter windows.

He said after the siege, a core group of the anarchists were seen returning to Westlake Plaza, changing from their all-black garb into street clothes and leaving the crowd.

Seattle police said two men were arrested. One of them was carrying a knife.

During the escalating violence, much of the activity was caught by KIRO 7 Eyewitness News cameras. The video showed the black-clad anarchists, with their faces covered, smashing in windows with rods at Niketown on Sixth Avenue, working in waves to break through the glass. A fire was set outside the building and paint splattered the remaining windows.

The protesters moved down the street in a destructive swath, breaking out windows at businesses and buildings on the way, including the old federal courthouse at Sixth Avenue and Spring Street, where a self-proclaimed superhero, similar to Pheonix Jones, was seen with his can of pepper spray. At times, the man was surrounded by the menacing figures during the mayhem.

Windows were also smashed at the Wells Fargo at Fourth and Seneca, and cars were also casualties of the melee.

Seattle police have established a non-emergency number for people whose car or business has suffered damage: 206-625-5011.

Recent online postings show that anarchists may have plans to target police, specifically officers riding on horseback.

Other postings have suggestions about how to conceal a weapon behind a protest sign.

Police urged business owners to remove items from the street that could be used as a weapon or set on fire.

McGinn said the majority of the protesters were peaceful and that the violent group was using the cover of crowds to cause property damage. He expressed concern that the group dressed in black might return for afternoon gatherings.

Many downtown businesses, such as Nordstrom and Bank of America, have gone into lockdown as a result of the violence. Others have opted to send their employees home for the rest of the day.

At about noon, before the violence broke out, helicopter video showed hundreds of people walking down Fourth Avenue. Again, many were dressed in black and some carried a banner sign that said "total freedom."

Video showed protesters surrounding a car that was trying to leave. One person climbed over it and others hit it with signs or their hands. Two men got out of the car and as officers arrived, it was finally allowed to leave.

At about 3 p.m., the protesters streamed down Fourth Avenue to Seattle Center where they may have rallied. They were later seen heading back downtown.

Thousands are expected to attend a May Day march that will start with a rally at a church in the Central District. Late in the afternoon, the group will head downtown to the Wells Fargo building between Second and Third avenues between Madison and Marion streets. Protesters are claiming the bank supports companies that build jails that detain immigrants. The Federal Building is on Second Avenue near Wells Fargo and is a customary gathering place for rallies.

The protests are expected to wreak havoc on late afternoon traffic, and the Seattle Department of Transportation and transit agencies are warning people to be prepared for major congestion and big delays downtown.

Several groups and organizations jumped in on Tuesday’s movement including Occupy Seattle demonstrators, immigration rights activists, students and a group of and bicyclists.